People who breathe polluted air experience changes in the brain regions that control emotions and are more likely to develop anxiety and depression as a result than those who breathe cleaner air. These are the key findings of a systematic review my colleagues and I recently published in the newspaper neurotoxicology.
Our interdisciplinary team reviewed more than 100 research articles from animal and human studies that focused on the effects of outdoor air pollution on mental health and the regions of the brain that regulate emotions. The three main brain regions we focused on were the hippocampus, the amygdala, and the prefrontal cortex.
In our analysis, 73% of the studies reported higher mental health symptoms and behaviors in humans and animals, such as rats, that were exposed to higher-than-average levels of air pollution. Some exposures that caused negative effects occurred in ranges of air pollution currently considered “safe” by the Environmental Protection Agency Standards.
In addition, we found that 95% of the studies that examined brain effects found significant physical and functional changes within brain regions that regulate emotions in people exposed to higher levels of air pollution.
Most of these studies found that exposure to elevated levels of air pollution is associated with increased inflammation and changes in the regulation of neurotransmitters, which act as chemical messengers in the brain.
why does it matter
Research has been done on the physical health effects associated with exposure to air pollution, such as asthma and respiratory problems. well documented for decades.
But only in the last 10 years have researchers begun to understand how air pollution can affect the brain. Studies have shown that small air pollutants, such as ultrafine particles from vehicle exhaust, can affect the brain either directlytraveling through the nose and into the brain, or indirectlyby causing inflammation and altered immune responses in the body that can then cross over to the brain.
At the same time, researchers are increasingly documenting the association between air pollution and its negative effects on mental health. Unfortunately, research suggests that air pollution will only get worse as climate change intensifies and carbon emissions remain not regulated.
For this reason, more research on the health effects of air pollution exposure that goes beyond respiratory health outcomes in the realm of biological psychiatry is urgently needed. For example, the neurobiological mechanisms through which air pollution increases the risk of mental health symptoms are not yet well understood.
What remains unknown
In addition to our main findings, our team also identified some notable gaps within the research that need to be addressed to get a fuller picture of the relationship between air pollution and brain health.
Relatively few studies have examined the effects of exposure to air pollution during the first years of life, such as infancy and childhood, and in childhood and adolescence. This is especially worrisome given that the brain continues to develop until early adulthood and therefore may be particularly susceptible to the effects of air pollution.
We also found that among the studies investigating the effects of air pollution on the brain, only 10 were conducted in humans. While animal research has amply shown that air pollution can cause a large number of changes within the animal brainResearch on how air pollution affects the human brain is much more limited.
Additionally, most of the existing brain studies in humans have focused on physical changes, such as differences in overall brain size. More research is needed based on a technique called functional brain imaging, which could allow researchers like us to detect subtle or smaller changes that can occur before physical changes.
In the future, our team plans to use brain imaging methods to study how air pollution increases the risk of anxiety during adolescence. We plan to use a variety of techniques, including personal air monitors that children can use as they go about their day, allowing us to more accurately assess their exposure.
Clara Zundel is a Postdoctoral Researcher in Psychiatry and Behavioral Neurosciences, Wayne State University.
This article first appeared on The conversation.
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